1. Field of the Invention
This invention relates to chemical analysis of fluids and, more specifically, to a method of obtaining a sample representative of the total contents of a container for analysis.
2. Brief Description of the Prior Art
Where solubility or miscibility is low, fluids, including both liquid and gases which can be either hazardous, non-hazardous or non-classified will ordinarily stratify into various thermal, density, composition and/or insoluble layers in a container. This is especially the case in bulk tanks where chemical mixtures are influenced by gravity as well as possibly for other reasons. Often, one chemical is not miscible with other chemicals such as, for example, a mixture of fuel oil, water and perchloroethylene. Such chemicals contained in the same tank would separate into three separate layers with the perchloroethylene on the bottom, water in the middle and the fuel oil on the top.
Often and almost always in the case of hazardous waste liquid materials that have stratified into layers, a representative sample of the non-homogeneous fluid is required for analysis and this analysis is intended to accurately represent the entire contents of the tank. Therefore, accuracy in extracting a proper sample to represent exactly the bulk liquid is critical and, to date, many means have been utilized to obtain a sample of such fluid for analysis. However, none of the prior art systems are capable of extracting a sample with the same composition proportions as the bulk liquid where stratification has occurred and this is especially true in the case of containers with non-uniform cross sections from top to bottom.
Prior art bulk liquid tank sampling techniques range from a valve in the bottom to drain off a sample into a jar, which only extracts off the bottom of the tank, to straight wall tubes dipped into the tank which extend from the top of the tank to the bottom thereof. In the latter case the tube bottom is open and the liquid enters the tube bottom on the way down and then the tube bottom is closed before the tube is withdrawn and the sample extracted. This latter method provides a reasonably accurate sample if the tank has straight flat vertical parallel walls or, in other words, uniform cross-section from top to bottom. However, this latter system generally is incapable of meeting the accuracy requirements for round horizontal tanks or other tanks that do not contain the same cross-sectional volume for each increment of variation in liquid height from center to top and center to bottom. Other prior art techniques involve extraction of a fixed amount (such as one cubic centimeter) of sample on a time interval basis from the output pipe as the bulk liquid is withdrawn. This method is very popular, however it involves numerous errors and variables and is not acceptable as an accurate, reliable procedure. The bulk extraction rate from the tank in not proportioned to the rate of change in volume of the tank (including all the various layers) as the tank is emptied for removal and disposal. No known attempts have been made to consider the radial effects of a tank on the sample quality and no available equipment is known to exist at present that proportions sample extraction with the corresponding bulk liquid tank volume to correct for the radial changes in the vertical walls of the tank.